U.S. patent application number 13/989188 was filed with the patent office on 2013-11-14 for block diene elastomer for rubber compositions that can be used in pneumatic tires.
This patent application is currently assigned to Michelin Recherche et Technique S.A.. The applicant listed for this patent is Jean-Michel Favrot, Jean Marc Marechal, Nathalie Simon. Invention is credited to Jean-Michel Favrot, Jean Marc Marechal, Nathalie Simon.
Application Number | 20130303685 13/989188 |
Document ID | / |
Family ID | 43528332 |
Filed Date | 2013-11-14 |
United States Patent
Application |
20130303685 |
Kind Code |
A1 |
Favrot; Jean-Michel ; et
al. |
November 14, 2013 |
BLOCK DIENE ELASTOMER FOR RUBBER COMPOSITIONS THAT CAN BE USED IN
PNEUMATIC TIRES
Abstract
The invention relates to a block diene elastomer corresponding
to the following formula: ##STR00001## where: n and m are each an
integer of greater than or equal to 0, such that n+m.gtoreq.1 and
n+m.ltoreq.20, each A block is composed of a polybutadiene, each B
block is composed of a diene elastomer, the molar content of units
resulting from conjugated dienes of which is greater than 15%, the
B blocks being identical to one another, X is an organic or
inorganic group which can comprise a functional group which
interacts with a reinforcing filler, the number-average molecular
weight Mn1 of each A block varies from 2 500 to 20 000 g/mol, the
number-average molecular weight Mn2 of each B block varies from 80
000 to 350 000 g/mol, and the content of 1,2-linkages in each A
block is between 1 and 20%.
Inventors: |
Favrot; Jean-Michel;
(Clermont-Ferrand Cedex 09, FR) ; Simon; Nathalie;
(Clermont-Ferrand Cedex, FR) ; Marechal; Jean Marc;
(Clermont-Ferrand Cedex, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Favrot; Jean-Michel
Simon; Nathalie
Marechal; Jean Marc |
Clermont-Ferrand Cedex 09
Clermont-Ferrand Cedex
Clermont-Ferrand Cedex |
|
FR
FR
FR |
|
|
Assignee: |
Michelin Recherche et Technique
S.A.
Granges-Paccot
CH
Compagnie Generale Des Etablissements Michelin
Clermont-Ferrand
FR
|
Family ID: |
43528332 |
Appl. No.: |
13/989188 |
Filed: |
November 23, 2011 |
PCT Filed: |
November 23, 2011 |
PCT NO: |
PCT/EP2011/070744 |
371 Date: |
July 30, 2013 |
Current U.S.
Class: |
524/572 ;
525/314 |
Current CPC
Class: |
B60C 1/00 20130101; C08F
297/04 20130101; C08F 299/00 20130101; C08C 19/42 20130101; C08L
53/005 20130101; C08F 297/02 20130101; C08C 19/26 20130101; C08L
53/02 20130101; C08C 19/44 20130101 |
Class at
Publication: |
524/572 ;
525/314 |
International
Class: |
C08F 299/00 20060101
C08F299/00; C08L 53/02 20060101 C08L053/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 23, 2010 |
FR |
1059643 |
Claims
1. Block diene elastomer corresponding to the following formula:
##STR00005## where: n and m are each an integer of greater than or
equal to 0, such that n+m.gtoreq.1 and n+m.ltoreq.20, each A block
is composed of a polybutadiene, each B block is composed of a diene
elastomer, the molar content of units resulting from conjugated
dienes of which is greater than 15%, the B blocks being identical
to one another, X is an organic or inorganic group which can
comprise a functional group which interacts with a reinforcing
filler, the number-average molecular weight Mn1 of each A block
varies from 2 500 to 20 000 g/mol, the number-average molecular
weight Mn2 of each B block varies from 80 000 to 350 000 g/mol, and
the content of 1,2-linkages in each A block is between 1 and
20%.
2. Block diene elastomer according to claim 1, wherein the ratio of
the said molecular weights Mn1/Mn2 is between 5 and 20%.
3. Block diene elastomer according to claim 1, wherein m+n varies
from 1 to 4.
4. Block diene elastomer according to claim 1, wherein the X block
comprises a functional group which interacts with a reinforcing
filler.
5. Block diene elastomer according to claim 4, wherein the said
functional group which interacts with the reinforcing filler
comprises a group chosen from the following groups: silanol, amine,
mono-, di- or trialkoxysilane, alkoxysilane bearing a primary,
secondary or tertiary amine functional group.
6. Block diene elastomer according to claim 4, wherein the said
functional group which interacts with the reinforcing filler
comprises a C--Sn bond.
7. Block diene elastomer according to claim 6, wherein the said
functional group which interacts with the reinforcing filler is
obtained by reaction with an agent of mono-, di-, tri- or
tetrahalotin type.
8. Block diene elastomer according to claim 1, wherein the B block
or blocks are chosen from polyisoprene, copolymers of styrene and
butadiene, copolymers of styrene and isoprene, copolymers of
butadiene and isoprene or styrene/butadiene/isoprene
terpolymers.
9. Crosslinkable or crosslinked rubber composition comprising an
elastomer matrix, wherein the elastomer matrix comprises a block
diene elastomer as defined in any one of the preceding claims.
10. Composition according to claim 9, wherein it comprises a
reinforcing filler.
11. Composition according to claim 9, wherein the composition
further comprises a chemical crosslinking agent.
12. Semi-finished article made of rubber for a tire, wherein it
comprises a crosslinkable or crosslinked rubber composition as
defined in claim 9.
13. Tire, wherein it comprises a semi-finished article as defined
in claim 12.
Description
BACKGROUND
[0001] 1. Field
[0002] The present invention relates to a specific block diene
elastomer, the end or ends of which are composed of a polybutadiene
block, intended to form an elastomer matrix of a crosslinkable
rubber composition of reduced hysteresis, to a rubber composition
in which it is present, to a semi-finished article in which it is
present and to a tire incorporating such a semi-finished
article.
[0003] 2. Description of Related Art
[0004] The reduction in the hysteresis of the mixtures is an
ongoing objective of the tire industry in order to limit the
consumption of petrol and to thus protect the environment. This
reduction in hysteresis must, however, be carried out while keeping
intact, indeed even while improving, the processability of the
mixtures.
[0005] Many solutions have already been experimented with in order
to achieve the objective of fall in hysteresis. In particular, the
functionalization of the polymers by a functional group which
interacts with the reinforcing filler has appeared as an
advantageous route.
[0006] Functional groups which interact with the filler have thus
been attached at the chain end at the start or end of
polymerization by means of functional initiators or
functionalization agents. By way of example,
4,4'-bis(diethylamino)benzophenone, also known as DEAB, or other
aminated functional groups which interact with carbon black have
been added at the end of polymerization, as described in the patent
documents FR 2 526 030 and U.S. Pat. No. 4,848,511. The polymers
coupled by or star-branched by tin comprise functional groups
capable of interacting with carbon black which are introduced at
the end of polymerization. Mention may be made, by way of example,
of the European patent document EP 0 709 235. Functional groups
which interact with silica have also been attached at the chain end
at the end of polymerization, such as functional groups comprising
a silanol group which are disclosed in the patent document FR 2 740
778 or functional groups comprising alkoxysilane or aryloxysilane
groups which are described in the document U.S. Pat. No. 5,066,721.
The majority of these solutions, both for the black and for the
silica, genuinely result in a limitation on hysteresis of the
corresponding compositions but concomitantly in a greater
difficulty in processing these same compositions.
[0007] Functional groups which interact with the filler have also
been added in the middle of the chain at the end of polymerization.
Mention may be made, by way of example, of patent document FR 2 930
554, which discloses aminoalkoxysilane functional groups located in
the middle of the chain. This solution results in improved
hysteresis and mechanical properties of the compositions in the
vulcanized state and in improved raw processing of these same
compositions.
[0008] Patent EP 1 278 789 describes a copolymer comprising n
blocks (n=2 or 3) intended to form an elastomer matrix of a
crosslinkable rubber composition, each of the said blocks
comprising an essentially unsaturated diene elastomer and one or
each of the said blocks forming a chain end of the said copolymer
being composed of a polyisoprene. The number-average molecular
weight of the polyisoprene block is between 2 500 and 20 000 g/mol
and the number-average molecular weight of the block of the
copolymer which is other than the said polyisoprene block is
substantially between 80 000 g/mol and 350 000 g/mol. The use of
the said block copolymer makes it possible to significantly
optimize the results of reduction in hysteresis and processability
for the said rubber composition in which it is present.
SUMMARY
[0009] The Applicant Company has discovered, surprisingly, that a
block diene elastomer corresponding to the following formula:
##STR00002##
[0010] where: [0011] n and m are each an integer of greater than or
equal to 0, such that n+m.gtoreq.1 and n+m.ltoreq.20, [0012] each A
block is composed of a polybutadiene, [0013] each B block is
composed of a diene elastomer, the molar content of units resulting
from conjugated dienes of which is greater than 15%, the B blocks
being identical to one another, [0014] X is an organic or inorganic
group which can comprise a functional group which interacts with a
reinforcing filler, [0015] the number-average molecular weight Mn1
of each A block varies from 2 500 to 20 000 g/mol, [0016] the
number-average molecular weight Mn2 of each B block varies from 80
000 to 350 000 g/mol, and [0017] the content of 1,2- linkages in
each A block is between 1 and 20%, makes possible a reduction in
the hysteresis of a rubber composition in which it is present while
retaining a processing acceptable for use in tires.
[0018] A subject-matter of the invention is thus a block diene
elastomer corresponding to the following formula:
##STR00003##
[0019] where: [0020] n and m are each an integer of greater than or
equal to 0, such that n+m.gtoreq.1 and n+m.ltoreq.20, [0021] each A
block is composed of a polybutadiene, [0022] each B block is
composed of a diene elastomer, the molar content of units resulting
from conjugated dienes of which is greater than 15%, the B blocks
being identical to one another, [0023] X is an organic or inorganic
group which can comprise a functional group which interacts with a
reinforcing filler, [0024] the number-average molecular weight Mn1
of each A block varies from 2 500 to 20 000 g/mol, [0025] the
number-average molecular weight Mn2 of each B block varies from 80
000 to 350 000 g/mol, and [0026] the content of 1,2- linkages in
the A block is between 1 and 20%.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0027] Preferably, the ratio of the molecular weights Mn1/Mn2 is
between 5 and 20%.
[0028] Preferably, m+n varies from 1 to 4. In other words, the
block diene elastomer according to the invention preferably
comprises from 1 to 4 A-B elastomer chains or branches (m, n and
A-B being defined as above).
[0029] "Essentially unsaturated" diene elastomer (i.e., the molar
content of units resulting from conjugated dienes of which is
greater than 15%) capable of being employed in order to obtain the
B block or blocks other than the polybutadiene block or blocks,
themselves corresponding to this definition, is understood to mean
any homopolymer obtained by polymerization of a conjugated diene
monomer having from 4 to 12 carbon atoms, or any block, random,
sequential or microsequential copolymer obtained by
copolymerization of one or more conjugated dienes with one another
or with one or more vinylaromatic compounds having from 8 to 20
carbon atoms.
[0030] The following are suitable in particular as conjugated
dienes: 1,3-butadiene, 2-methyl-1,3-butadiene,
2,3-di(C.sub.1-C.sub.5 alkyl)-1,3-butadienes, such as, for example,
2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene,
2-methyl-3-ethyl-1,3-butadiene or
2-methyl-3-isopropyl-1,3-butadiene, an aryl-1,3-butadiene,
1,3-pentadiene or 2,4-hexadiene. The following, for example, are
suitable as vinylaromatic compounds: styrene, ortho-, meta- or
para-methylstyrene, the "vinyltoluene" commercial mixture,
para-(tert-butyl)styrene, methoxystyrenes, chlorostyrenes,
vinylmesitylene, divinylbenzene or vinylnaphthalene.
[0031] Preferably, the B block or blocks are chosen from copolymers
of styrene and butadiene, copolymers of styrene and isoprene,
copolymers of butadiene and isoprene, styrene/butadiene/isoprene
terpolymers and polyisoprene.
[0032] The following are suitable: polyisoprenes, butadiene/styrene
copolymers and in particular those having a Tg (glass transition
temperature Tg, measured according to ASTM D3418) of between
0.degree. C. and -70.degree. C. and more particularly between
-10.degree. C. and -60.degree. C., a styrene content of between 5%
and 60% by weight and more particularly between 20% and 50%, a
content (mol %) of 1,2- bonds of the butadiene part of between 4%
and 75% and a content (mol %) of trans-1,4- bonds of between 10%
and 80%, butadiene/isoprene copolymers, in particular those having
an isoprene content of between 5% and 90% by weight and a Tg of
-40.degree. C. to -80.degree. C., or isoprene/styrene copolymers,
in particular those having a styrene content of between 5% and 50%
by weight and a Tg of between 5.degree. C. and -55.degree. C.
[0033] In the case of butadiene/styrene/isoprene copolymers, those
having a styrene content of between 5% and 50% by weight and more
particularly of between 10% and 40%, an isoprene content of between
15% and 60% by weight and more particularly between 20% and 50%, a
butadiene content of between 5% and 50% by weight and more
particularly of between 20% and 40%, a content (mol %) of 1,2-
units of the butadiene part of between 4% and 85%, a content (mol
%) of trans-1,4- units of the butadiene part of between 6% and 80%,
a content (mol %) of 1,2- plus 3,4- units of the isoprene part of
between 5% and 70% and a content (mol %) of trans-1,4- units of the
isoprene part of between 10% and 50%, and more generally any
butadiene/styrene/isoprene copolymer having a Tg of between
-5.degree. C. and -70.degree. C., are suitable in particular.
[0034] According to a first embodiment of the invention, the B
block or blocks are copolymers of styrene and butadiene.
[0035] According to a second embodiment of the invention, the B
block or blocks are copolymers of styrene and isoprene.
[0036] Preferably, the X group comprises a functional group which
interacts with a reinforcing filler.
[0037] Preferably, the functional group which interacts with the
reinforcing filler comprises a group chosen from the following
groups: silanol, mono-, di- or trialkoxysilane or alkoxysilane
bearing a primary, secondary or tertiary amine functional group.
Alternatively, the functional group which interacts with the
reinforcing filler comprises a C--Sn bond.
[0038] The interactive functional group comprising a C--Sn bond can
be obtained with a monohalotin functionalization agent or a
dihalotin coupling agent which can correspond to the general
formula R.sub.4-xSnX.sup.0.sub.x, where x represents an integer
having the value 1 or 2, R represents an alkyl, cycloalkyl, aryl,
alkaryl or vinyl radical having from 1 to 12 carbon atoms,
preferably a butyl, and X.sup.0 is a halogen atom, preferably
chlorine. Mention may be made, as preferred functionalization
agent, of tributyltin monochloride or dibutyltin dichloride. In the
same way, the functionalization can be obtained with a tin-derived
functionalization agent which can correspond to the general formula
(X.sup.1.sub.yR.sup.1.sub.3-ySn)--O--(SnR.sup.1.sub.3-zX.sup.1.su-
b.z) or
(X.sup.1.sub.yR.sup.1.sub.3-ySn)--O--(CH.sub.2).sub.e--O--(SnR.sup-
.1.sub.3-zX.sup.1.sub.z), where y and z represent integers varying
from 0 to 2 and y+z is equal to 1 or 2, R.sup.1 represents an
alkyl, cycloalkyl, aryl, alkaryl or vinyl radical having from 1 to
12 carbon atoms, preferably a butyl, X.sup.1 is a halogen atom,
preferably chlorine, and e represents an integer from 1 to 20,
preferably 4.
[0039] This interactive functional group can also be obtained with
a tri- or tetrahalotin star-branching agent which can correspond to
the formula R.sup.2.sub.qSnX.sup.2.sub.4-q, where q represents an
integer having the value 0 or 1, R.sup.2 represents an alkyl,
cycloalkyl, aryl, alkaryl or vinyl radical having from 1 to 12
carbon atoms, preferably a butyl, and X.sup.2 is a halogen atom,
preferably chlorine. Mention may be made, as preferred
star-branching agent, of butyltin trichloride or tin tetrachloride.
In the same way, the star-branching can be obtained with a
tin-derived functionalization agent which can correspond to the
general formula
(X.sup.3.sub.kR.sup.3.sub.3-kSn)--O--(SnR.sup.3.sub.3-1X.sup.3.su-
b.1) or
(X.sup.3.sub.kR.sup.3.sub.3-kSn)--O--(CH.sub.2).sub.f--O--(SnR.sup-
.3.sub.3-1X.sup.3.sub.1), where k and 1 represent integers varying
from 0 to 3, k+1 varying from 3 to 6, R.sup.3 represents an alkyl,
cycloalkyl, aryl, alkaryl or vinyl radical having from 1 to 12
carbon atoms, preferably a butyl, X.sup.3 is a halogen atom,
preferably chlorine, and f represents an integer having a value
from 1 to 20, preferably 4.
[0040] The said interactive functional group can also comprise an
amine group, which can be obtained, for example, with a
functionalization agent, such as
4,4'-bis(diethylamino)benzophenone, also known as DEAB.
[0041] Thus, a preferred block diene elastomer according to the
invention is such that the B block or blocks are copolymers of
styrene and butadiene and X is an organic or inorganic group
comprising a functional group which interacts with silica or carbon
black, and n+m varies from 1 to 4.
[0042] More preferably still, the B block or blocks are copolymers
of styrene and butadiene and X is interactive with carbon black and
it can, for example, comprise a C--Sn bond, it being possible for
the Sn functionalization to be obtained with a functionalization,
coupling or star-branching agent as defined above, and n+m varies
from 1 to 4.
[0043] The elastomer according to the invention is generally
synthesized by anionic polymerization initiated by an initiator.
Use may be made, as polymerization initiator, of any known
monofunctional anionic initiator. Mention may in particular be made
of organolithium initiators, in particular those comprising a
carbon-lithium bond. Representative compounds are aliphatic
organolithium compounds, such as ethyllithium, n-butyllithium
(n-BuLi), isobutyllithium and dilithium polymethylenes, such as
1,4-dilithiobutane.
[0044] The polymerization is, as known per se, preferably carried
out in the presence of an inert solvent which can, for example, be
an aliphatic or alicyclic hydrocarbon, such as pentane, hexane,
heptane, isooctane or cyclohexane, or an aromatic hydrocarbon, such
as benzene, toluene or xylene.
[0045] The polymerization can be carried out continuously or
batchwise. The polymerization is generally carried out at a
temperature of between 20.degree. C. and 120.degree. C. and
preferably in the vicinity of 30.degree. C. to 90.degree. C. It is,
of course, also possible to add, at the end of polymerization, a
transmetallation agent for mollifying the reactivity of the living
chain end.
[0046] When the block diene elastomer according to the invention
comprises a functional group which interacts with a reinforcing
filler, the functionalized elastomer can be obtained in a way known
per se by reaction of a functionalization or coupling or
star-branching agent with the living diene elastomer resulting from
the polymerization.
[0047] A further subject-matter of the invention is a crosslinkable
or crosslinked rubber composition comprising an elastomer matrix,
the elastomer matrix comprising a block diene elastomer according
to the invention.
[0048] The composition can comprise from 1 to 100 phr of block
diene elastomer according to the invention.
[0049] The composition according to the invention can also comprise
at least one diene elastomer other than the said block elastomer
according to the invention. This or these diene elastomers other
than the block elastomer according to the invention can be chosen
from the diene elastomers conventionally used in tires, such as
natural rubber or a synthetic elastomer, or also another
functionalized or star-branched elastomer.
[0050] The composition according to the invention can comprise a
reinforcing filler.
[0051] Use may also be made of any type of reinforcing filler known
for its abilities to reinforce a rubber composition which can be
used for the manufacture of tires, for example a reinforcing
organic filler, such as carbon black, a reinforcing inorganic
filler, such as silica, or also a blend of these two types of
filler, in particular a blend of carbon black and silica.
[0052] All carbon blacks, in particular blacks of the HAF, ISAF or
SAF type, conventionally used in tires ("tire-grade" blacks), are
suitable as carbon blacks. Mention will more particularly be made,
among the latter, of the reinforcing carbon blacks of the 100, 200
or 300 series (ASTM grades), such as, for example, the N115, N134,
N234, N326, N330, N339, N347 or N375 blacks. Use may also be made,
according to the applications targeted, of blacks of higher series
FF, FEF, GPF or SRF, for example the N660, N683 or N772 blacks. The
carbon blacks might, for example, be already incorporated in the
isoprene elastomer in the form of a masterbatch (see, for example,
Applications WO 97/36724 or WO 99/16600).
[0053] Mention may be made, as examples of organic fillers other
than carbon blacks, of functionalized polyvinylaromatic organic
fillers, such as described in Applications WO-A-2006/069792 and
WO-A-2006/069793.
[0054] The term "reinforcing inorganic filler" should be
understood, in the present patent application, by definition, as
meaning any inorganic or mineral filler, whatever its colour and
its origin (natural or synthetic), also known as "white filler",
"clear filler" or indeed even "non-black filler", in contrast to
carbon black, capable of reinforcing by itself alone, without means
other than an intermediate coupling agent, a rubber composition
intended for the manufacture of tires, in other words capable of
replacing, in its reinforcing role, a conventional tire-grade
carbon black; such a filler is generally characterized, in a known
way, by the presence of hydroxyl (--OH) groups at its surface.
[0055] The physical state under which the reinforcing inorganic
filler is provided is not important, whether it is in the form of a
powder, of microbeads, of granules, of beads or any other
appropriate densified form. Of course, the term "reinforcing
inorganic filler" is also understood to mean mixtures of different
reinforcing inorganic fillers, in particular of highly dispersible
siliceous and/or aluminous fillers as described below.
[0056] Mineral fillers of the siliceous type, in particular silica
(SiO.sub.2), or of the aluminous type, in particular alumina
(Al.sub.2O.sub.3), are suitable in particular as reinforcing
inorganic fillers. The silica used can be any reinforcing silica
known to a person skilled in the art, in particular any
precipitated or fumed silica exhibiting a BET specific surface and
a CTAB specific surface both of less than 450 m.sup.2/g, preferably
from to 400 m.sup.2/g. Mention will be made, as highly dispersible
precipitated silicas ("HDSs"), for example, of the Ultrasil 7000
and Ultrasil 7005 silicas from Degussa, the Zeosil 1165 MP, 1135 MP
and 1115 MP silicas from Rhodia, the Hi-Sil EZ150G silica from PPG,
the Zeopol 8715, 8745 and 8755 silicas from Huber or the silicas
with a high specific surface as described in Application WO
03/16837.
[0057] When the composition according to the invention is intended
for tire treads having a low rolling resistance, the reinforcing
inorganic filler used, in particular if it is silica, preferably
has a BET specific surface of between 45 and 400 m.sup.2/g, more
preferably of between 60 and 300 m.sup.2/g.
[0058] Preferably, the content of reinforcing filler in the
composition is between 30 and 150 phr, more preferably between 50
and 120 phr. The optimum is different according to the specific
applications targeted: the expected level of reinforcement with
regard to a bicycle tire, for example, is, of course, lower than
that required with regard to a tire capable of running at high
speed in a sustained manner, for example a motorcycle tire, a tire
for a passenger vehicle or a tire for a utility vehicle, such as a
heavy-duty vehicle.
[0059] According to one embodiment, the reinforcing filler
predominantly comprises silica, the content of carbon black present
in the composition preferably being between 2 and 20 phr.
[0060] According to another embodiment of the invention, the
reinforcing filler predominantly comprises carbon black.
[0061] Use is made, in a known manner, in order to couple the
reinforcing inorganic filler to the diene elastomer, of an at least
bifunctional coupling agent (or bonding agent) intended to provide
a satisfactory connection, of chemical and/or physical nature,
between the inorganic filler (surface of its particles) and the
diene elastomer, in particular bifunctional organosilanes or
polyorganosiloxanes.
[0062] Use is made in particular of silane polysulphides, referred
to as "symmetrical" or "unsymmetrical" depending on their specific
structure, such as described, for example, in Applications WO
03/002648 (or US 2005/016651) and WO 03/002649 (or US
2005/016650).
[0063] Suitable in particular, without the definition below being
limiting, are silane polysulphides known as "symmetrical",
corresponding to the following general formula (III):
Z-A-S.sub.x-A-Z, in which: (III) [0064] x is an integer from 2 to 8
(preferably from 2 to 5); [0065] A is a divalent hydrocarbon
radical (preferably C.sub.1-C.sub.18 alkylene groups or
C.sub.6-C.sub.12 arylene groups, more particularly
C.sub.1-C.sub.10, in particular C.sub.1-C.sub.4, alkylenes, in
particular propylene); [0066] Z corresponds to one of the formulae
below:
##STR00004##
[0067] in which: [0068] the R.sup.1 radicals, which are substituted
or unsubstituted and identical to or different from one another,
represent a C.sub.1-C.sub.18 alkyl group, a C.sub.5-C.sub.18
cycloalkyl group or a C.sub.6-C.sub.18 aryl group (preferably
C.sub.1-C.sub.6 alkyl, cyclohexyl or phenyl groups, in particular
C.sub.1-C.sub.4 alkyl groups, more particularly methyl and/or
ethyl); [0069] the R.sup.2 radicals, which are substituted or
unsubstituted and identical to or different from one another,
represent a C.sub.1-C.sub.18 alkoxyl group or a C.sub.5-C.sub.18
cycloalkoxyl group (preferably a group chosen from C.sub.1-C.sub.8
alkoxyls and C.sub.5-C.sub.8 cycloalkoxyls, more preferably still a
group chosen from C.sub.1-C.sub.4 alkoxyls, in particular methoxyl
and ethoxyl).
[0070] In the case of a mixture of alkoxysilane polysulphides
corresponding to the above formula (III), in particular normal
commercially available mixtures, the mean value of the "x" indices
is a fractional number preferably of between 2 and 5, more
preferably of approximately 4. However, the invention can also
advantageously be carried out, for example, with alkoxysilane
disulphides (x=2).
[0071] Mention will more particularly be made, as examples of
silane polysulphides, of
bis((C.sub.1-C.sub.4)alkoxyl(C.sub.1-C.sub.4)alkylsilyl(C.sub.1-C.sub.4)a-
lkyl)polysulphides (in particular disulphides, trisulphides or
tetrasulphides), such as, for example, bis(3-trimethoxysilylpropyl)
or bis(3-triethoxysilylpropyl)polysulphides. Use is in particular
made, among these compounds, of
bis(3-triethoxysilylpropyl)tetrasulphide, abbreviated to TESPT, of
formula [(C.sub.2H.sub.5O).sub.3Si(CH.sub.2).sub.3S.sub.2].sub.2,
or bis(triethoxysilylpropyl)disulphide, abbreviated to TESPD, of
formula [(C.sub.2H.sub.SO).sub.3Si(CH.sub.2).sub.3S].sub.2. Mention
will also be made, as preferred examples, of
bis(mono(C.sub.1-C.sub.4)alkoxyldi(C.sub.1-C.sub.4)alkylsilylpropyl)polys-
ulphides (in particular disulphides, trisulphides or
tetrasulphides), more particularly
bis(monoethoxydimethylsilylpropyl)tetrasulphide, such as described
in Patent Application WO 02/083782 (or US 2004/132880).
[0072] Mention will in particular be made, as coupling agent other
than an alkoxysilane polysulphide, of bifunctional POSs
(polyorganosiloxanes) or else of hydroxysilane polysulphides
(R.sup.2.dbd.OH in the above formula III), such as described in
Patent Applications WO 02/30939 (or U.S. Pat. No. 6,774,255) and WO
02/31041 (or US 2004/051210), or else of silanes or POSs carrying
azodicarbonyl functional groups, such as described, for example, in
Patent Applications WO 2006/125532, WO 2006/125533, WO 2006/125534
and WO 2009/062733.
[0073] In the rubber composition, the content of coupling agent is
preferably between 4 and 12 phr, more preferably between 3 and 8
phr.
[0074] A person skilled in the art will understand that a
reinforcing filler of another nature, in particular organic nature,
might be used as filler equivalent to the reinforcing inorganic
filler described in the present section, provided that this
reinforcing filler is covered with an inorganic layer, such as
silica, or else comprises, at its surface, functional sites, in
particular hydroxyls, requiring the use of a coupling agent in
order to form the connection between the filler and the
elastomer.
[0075] The composition according to the invention can also comprise
a chemical crosslinking agent.
[0076] The chemical crosslinking makes possible the formation of
covalent bonds between the elastomer chains. The chemical
crosslinking can be carried out using a vulcanization system or
else using peroxide compounds.
[0077] The vulcanization system proper is based on sulphur (or on a
sulphur-donating agent) and on a primary vulcanization accelerator.
Additional to this base vulcanization system are various known
secondary vulcanization accelerators or vulcanization activators,
such as zinc oxide, stearic acid or equivalent compounds, or
guanidine derivatives (in particular diphenylguanidine),
incorporated during the first non-productive phase and/or during
the productive phase, as described subsequently.
[0078] The sulphur is used at a preferred content of between 0.5
and 12 phr, in particular between 1 and 10 phr. The primary
vulcanization accelerator is used at a preferred content of between
0.5 and 10 phr, more preferably of between 0.5 and 5.0 phr.
[0079] Use may be made, as (primary or secondary) accelerator, of
any compound capable of acting as accelerator for the vulcanization
of diene elastomers in the presence of sulphur, in particular
accelerators of the thiazole type, and also their derivatives, and
accelerators of thiuram and zinc dithiocarbamate types. These
accelerators are, for example, selected from the group consisting
of 2-mercaptobenzothiazyl disulphide (abbreviated to "MBTS"),
tetrabenzylthiuram disulphide ("TBZTD"),
N-cyclohexyl-2-benzothiazolesulphenamide ("CBS"),
N,N-dicyclohexyl-2-benzothiazolesulphenamide ("DCBS"),
N-(tert-butyl)-2-benzothiazolesulphenamide ("TBBS"),
N-(tert-butyl)-2-benzothiazolesulphenimide ("TBSI"), zinc
dibenzyldithiocarbamate ("ZBEC") and the mixtures of these
compounds.
[0080] Preferably, use is made of a primary accelerator of the
sulphenamide type.
[0081] When the chemical crosslinking is carried out using one or
more peroxide compounds, the said peroxide compound or compounds
represent from 0.01 to 10 phr.
[0082] Mention may be made, as peroxide compounds which can be used
as chemical crosslinking system, of acyl peroxides, for example
benzoyl peroxide or p-chlorobenzoyl peroxide, ketone peroxides, for
example methyl ethyl ketone peroxide, peroxyesters, for example
t-butyl peroxyacetate, t-butyl peroxybenzoate and t-butyl
peroxyphthalate, alkyl peroxides, for example dicumyl peroxide,
di(t-butyl) peroxybenzoate and
1,3-bis(t-butylperoxyisopropyl)benzene, or hydroperoxides, for
example t-butyl hydroperoxide.
[0083] The rubber composition according to the invention can also
comprise all or a portion of the usual additives generally used in
elastomer compositions intended for the manufacture of tires, in
particular of treads, such as, for example, plasticizers or
extending oils, whether the latter are of aromatic or non-aromatic
nature, pigments, protection agents, such as antiozone waxes (such
as Cire Ozone C32 ST), chemical antiozonants or antioxidants (such
as 6-PPD), antifatigue agents, reinforcing resins, methylene
acceptors (for example, phenolic novolak resin) or methylene donors
(for example, HMT or H3M), as described, for example, in
Application WO 02/10269, or adhesion promoters (cobalt salts, for
example).
[0084] Preferably, the composition according to the invention
comprises, as preferred non-aromatic or very weakly aromatic
plasticizing agent, at least one compound chosen from the group
consisting of naphthenic oils, paraffinic oils, MES oils, TDAE
oils, glycerol esters (in particular trioleates), plasticizing
hydrocarbon resins exhibiting a high Tg preferably of greater than
30.degree. C., and mixtures of such compounds.
[0085] The composition according to the invention can also
comprise, in addition to the coupling agents, activators of the
coupling of the reinforcing inorganic filler or more generally
processing aids capable, in a known way, by virtue of an
improvement in the dispersion of the inorganic filler in the rubber
matrix and of a lowering in the viscosity of the compositions, of
improving their ease of processing in the raw state, these
processing aids being, for example, hydrolysable silanes, such as
alkylalkoxysilanes (in particular alkyltriethoxysilanes), polyols,
polyethers (for example, polyethylene glycols), primary, secondary
or tertiary amines (for example, trialkanolamines), hydroxylated or
hydrolysable POSs, for example
.alpha.,.omega.-dihydroxypolyorganosiloxanes (in particular
.alpha.,.omega.-dihydroxypolydimethylsiloxanes), or fatty acids,
such as, for example, stearic acid.
[0086] The rubber composition according to the invention is
manufactured in appropriate mixers, using two successive phases of
preparation according to a general procedure well known to those
skilled in the art: a first phase of thermomechanical working or
kneading (sometimes referred to as "non-productive" phase) at high
temperature, up to a maximum temperature of between 130.degree. C.
and 200.degree. C., preferably between 145.degree. C. and
185.degree. C., followed by a second phase of mechanical working
(sometimes referred to as "productive" phase) at lower temperature,
typically below 120.degree. C., for example between 60.degree. C.
and 100.degree. C., during which finishing phase the chemical
crosslinking agent is incorporated.
[0087] According to a preferred embodiment of the invention, all
the base constituents of the composition according to the
invention, with the exception of the chemical crosslinking agent,
namely in particular the reinforcing filler or fillers and the
coupling agent, if appropriate, are intimately incorporated, by
kneading, in the block diene elastomer according to the invention
and in the other diene elastomers, if appropriate, during the first
"non-productive" phase, that is to say that at least these various
base constituents are introduced into the mixer and are
thermomechanically kneaded, in one or more stages, until the
maximum temperature of between 130.degree. C. and 200.degree. C.,
preferably of between 145.degree. C. and 185.degree. C., is
reached.
[0088] By way of example, the first (non-productive) phase is
carried out in a single thermomechanical stage during which all the
necessary constituents, the optional supplementary processing aids
and various other additives, with the exception of the chemical
cros slinking agent, are introduced into an appropriate mixer, such
as an ordinary internal mixer. The total duration of the kneading,
in this non-productive phase, is preferably between 1 and 15 min.
After cooling the mixture thus obtained during the first
non-productive phase, the chemical crosslinking agent is then
incorporated at low temperature, generally in an external mixer,
such as an open mill; everything is then mixed (productive phase)
for a few minutes, for example between 2 and 15 min.
[0089] The final composition thus obtained is subsequently
calendered, for example in the form of a sheet or plaque, in
particular for laboratory characterization, or else extruded in the
form of a rubber profiled element which can be used, for example,
as a tire tread for a passenger vehicle.
[0090] A further subject-matter of the invention is a semi-finished
article made of rubber for a tire, comprising the crosslinked or
crosslinkable rubber composition according to the invention.
Preferably, the said article is a tread.
[0091] A final subject-matter of the invention is a tire comprising
a semi-finished article according to the invention.
[0092] The invention is illustrated by the following examples.
EXAMPLES
1--Preparation of an Elastomer Matrix According to the
Invention
1.1--Measurements and Tests Used--Experimental Techniques Used for
the Pre-Curing Characterization of the Polymers Obtained
[0093] (a) Determination of the molar mass distribution by the size
exclusion chromatography (conventional SEC) technique
[0094] Size exclusion chromatography or SEC makes it possible to
separate macromolecules in solution according to their size through
columns filled with a porous gel. The macromolecules are separated
according to their hydrodynamic volume, the bulkiest being eluted
first.
[0095] Without being an absolute method, SEC makes it possible to
comprehend the distribution of the molar masses of a polymer. The
various number-average molar masses (Mn) and weight-average molar
masses (Mw) and the (Wp) weight at the peak can be determined from
commercial standard products and the polydispersity index
(PI=Mw/Mn) can be calculated via a "Moore" calibration.
[0096] (1) Preparation of the Polymer:
[0097] There is no specific treatment of the polymer sample before
analysis. The latter is simply dissolved in tetrahydrofuran at a
concentration of approximately 1 g/l. The solution is then filtered
through a filter with a porosity of 0.45 .mu.m before
injection.
[0098] (2) SEC Analysis:
[0099] The apparatus used is a "Waters Alliance" chromatograph. The
elution solvent is tetrahydrofuran, the flow rate is 0.7 ml/min,
the temperature of the system is 35.degree. C. and the analytical
time is 90 min. A set of four Waters columns in series, with
commercial names "Styragel HMW7", "Styragel HMW6E" and two
"Styragel HT6E", is used.
[0100] The volume of the solution of the polymer sample injected is
100 .mu.l. The detector is a "Waters 2410" differential
refractometer and the software for making use of the
chromatographic data is the "Waters Empower" system.
[0101] The calculated average molar masses relate to a calibration
curve produced with polystyrene standards having known molar
masses.
[0102] (b) For the polymers and rubber compositions, the Mooney
viscosities ML (1+4) at 100.degree. C. are measured according to
Standard ASTM D-1646.
[0103] Use is made of an oscillating consistometer as described in
Standard ASTM D-1646. The Mooney plasticity measurement is carried
out according to the following principle: the composition in the
raw state (i.e., before curing) is moulded in a cylindrical chamber
heated to 100.degree. C. After preheating for one minute, the rotor
rotates within the test specimen at 2 revolutions/minute and the
working torque for maintaining this movement is measured after
rotating for 4 minutes. The Mooney plasticity (ML 1+4) is expressed
in "Mooney unit" (MU, with 1 MU=0.83 N.m).
[0104] (c) The glass transition temperatures Tg of the polymers are
measured according to Standard ASTM D3418-03 using a differential
scanning calorimeter.
[0105] (d) Near-infrared spectroscopy (NIR) is used to
quantitatively determine the content by weight of styrene in the
elastomer and its microstructure (relative distribution of the
1,2-vinyl, trans-1,4 and cis-1,4 butadiene units). The principle of
the method is based on the Beer-Lambert law generalized for a
multicomponent system. As the method is indirect, it involves a
multivariate calibration [Vilmin, F., Dussap, C. and Coste, N.,
Applied Spectroscopy, 2006, 60, 619-29] carried out using standard
elastomers having a composition determined by .sup.13C NMR. The
styrene content and the microstructure are then calculated from the
NIR spectrum of an elastomer film having a thickness of
approximately 730 .mu.m. The spectrum is acquired in transmission
mode between 4000 and 6200 cm.sup.-1 with a resolution of 2
cm.sup.-1 using a Bruker Tensor 37 Fourier-transform near-infrared
spectrometer equipped with an InGaAs detector cooled by the Peltier
effect.
[0106] (e) For the polymers, the intrinsic viscosity at 25.degree.
C. of a 0.1 g/dl solution of polymer in toluene is measured
starting from a solution of dry polymer:
[0107] The intrinsic viscosity is determined by the measurement of
the flow time t of the polymer solution and of the flow time
t.sub.o of the toluene in a capillary tube.
[0108] The flow time of the toluene and the flow time of the 0.1
g/dl polymer solution are measured in an Ubbelohde tube (diameter
of the capillary 0.46 mm, capacity from 18 to 22 ml) placed in a
bath thermostatically controlled at 25.+-.0.1.degree. C.
[0109] The intrinsic viscosity is obtained by the following
relationship:
.eta. inh = 1 C ln [ ( t ) ( t O ) ] ##EQU00001##
[0110] with:
[0111] C: concentration of the toluene solution of polymer in
g/dl;
[0112] t: flow time of the toluene solution of polymer in
seconds;
[0113] t.sub.o: flow time of the toluene in seconds;
[0114] .eta..sub.inh: intrinsic viscosity, expressed in dl/g.
1.2--Preparation of an Elastomer A: Control Functionalized
Copolymer (Denoted SBR A)
[0115] (a) Copolymerization of Butadiene and Styrene:
[0116] The control copolymer batchwise in a reactor with a reaction
volume of 75 l, under nitrogen pressure, which reactor is equipped
with a stirrer of turbine type. Cyclohexane, butadiene and styrene
are introduced into this reactor according to respective
proportions by weight of 100/10/6.6. 500 parts per million (by
weight) of tetrahydrofuran (THF), as agent promoting vinyl bonds,
are also added to this reactor.
[0117] An amount of 45 .mu.mol of active n-butyllithium (n-BuLi)
per 100 g of solution is introduced into the reactor in order to
neutralize the protic impurities which are contributed by the
various constituents present in the reactor.
[0118] 650 .mu.mol of n-BuLi, representing the amount of active
initiator in order to initiate the polymerization, are
introduced.
[0119] The temperature of the reactor is maintained at 50.degree.
C. and, after a polymerization time of 60 min, the conversion of
monomers is 74%.
[0120] 312 .mu.mol/100 g of monomers of a functionalization agent
consisting of dibutyldichlorotin are subsequently added to the same
reactor. The functionalization reaction is carried out at
50.degree. C. After 15 min of this coupling reaction, the copolymer
thus functionalized is subjected to an anti-oxidizing treatment
using 0.8 phr of 2,2'-methylenebis(4-methyl-6-(tert-butyl)phenol)
and 0.2 phr of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine.
Any reaction is stopped by the addition of 1.5 lithium equivalents
of methanol.
[0121] The copolymer thus treated is separated from its solution by
a steam stripping operation and is then dried on a screw machine at
150.degree. C. for 15 sec, in order to obtain the control
functionalized copolymer A.
[0122] The intrinsic viscosity of this copolymer A is 1.94 dl/g and
its ML viscosity is 83.
[0123] This copolymer A comprises 28% of styrene (by weight) and,
for its butadiene part, 2.8% of vinyl units and the glass
transition temperature Tg of this copolymer A is -47.7.degree.
C.
[0124] The number-average molecular weight and the polydispersity
index of this copolymer A, which are determined by conventional
SEC, are 183 732 g/mol and 1.18 respectively.
1.3--Preparation of a B Elastomer (Denoted SBR B): Functionalized
Copolymer Comprising Three Blocks According to the Invention
[0125] (a) Preparation of a Living Polybutadiene:
[0126] The living polybutadiene is prepared batchwise in a bottle
with a capacity of 750 ml. On the one hand, 320 ml of
methylcyclohexane and 80 ml of butadiene according to the
respective ratios by weight of 100/20 and, on the other hand, an
amount of 10 000 .mu.mol of active sec-butyllithium (s-BuLi) per
100 g of butadiene are introduced into this bottle.
[0127] The polymerization is carried out at 70.degree. C. and,
after a reaction time of 12 min, the butadiene conversion is 100%.
This living polybutadiene thus obtained is stored in a freezer in
order to be used at a later date.
[0128] A second bottle is prepared in parallel by the same
procedure and stopped by one lithium equivalent of methanol in
order to characterize the polybutadiene thus obtained. The
number-average molecular weight, which is determined by
conventional SEC, is 109 437 g/mol. The content of 1,2- linkages is
10%.
[0129] (b) Copolymerization of Butadiene and Styrene Initiated by
This Living Polybutadiene:
[0130] The block copolymer other than the said living polybutadiene
is prepared batchwise in a reactor with a capacity of 10 l, under
nitrogen pressure, which reactor is equipped with a stirrer of
turbine type. 6200 ml of methylcyclohexane, 689 ml of butadiene and
387 ml of styrene are introduced into this reactor according to
respective proportions by weight of 100/9.2/7.3. 550 parts per
million (by weight) of tetrahydrofuran (THF), as agent promoting
vinyl bonds, are also added to this reactor.
[0131] An amount of 1500 .mu.mol of active n-butyllithium (n-BuLi)
is introduced into the reactor in order to neutralize the protic
impurities which are contributed by the various constituents
present in the reactor with the aim of limiting the formation of
dead or deactivated polybutadiene during the introduction of the
living polybutadiene solution into the reactor.
[0132] All of the living polybutadiene prepared in the preceding
stage described in section (a) of chapter 1-2), representing the
amount of active initiator for initiating the polymerization, is
introduced.
[0133] The temperature of the reactor is maintained at 50.degree.
C. and, after a polymerization time of 55 min, the conversion of
monomers is 70%.
[0134] The intrinsic viscosity of the copolymer before
functionalization, measured on a withdrawn sample stopped by one
lithium equivalent of methanol, is 1.35 dl/g and the number-average
molecular weight and the polydispersity index of the same withdrawn
sample, which are determined by conventional SEC, are 109 437 g/mol
and 1.15 respectively.
[0135] 2496 .mu.mol/100 g of monomers of a functionalization agent
consisting of dibutyldichlorotin are subsequently added to the same
reactor. The functionalization reaction is carried out at
60.degree. C. After 30 min of this coupling reaction, the block
copolymer thus functionalized is subjected to an anti-oxidizing
treatment using 0.8 phr of
2,2'-methylenebis(4-methyl-6-(tert-butyl)phenol) and 0.2 phr of
N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine. Any reaction is
stopped by the addition of 1.5 lithium equivalents of methanol.
[0136] The copolymer thus treated is separated from its solution by
a steam stripping operation, is then superficially dried on an open
mill at 100.degree. C. for approximately 5 min and is dried in an
oven at 60.degree. C. under vacuum and under a stream of nitrogen
for approximately 4 hours, in order to obtain the functionalized
block copolymer B according to the invention.
[0137] The intrinsic viscosity of this copolymer B is 2.09 dl/g and
its ML viscosity is 87.
[0138] The SBR block of this copolymer B comprises 28.6% of styrene
(by weight) and, for its butadiene part, 22.1% of vinyl units and
the glass transition temperature Tg of this copolymer B is
-49.degree. C.
[0139] The number-average molecular weight and the polydispersity
index of this copolymer B, which are determined by conventional
SEC, are 175 489 g/mol and 1.28 respectively.
2--Comparative Examples of Rubber Compositions
2.1--Measurements and Tests Used
[0140] a) The Mooney viscosity ML (large rotor) or MS (small rotor)
(1+4) at 100.degree. C.: measured according to Standard ASTM:
D-1646, entitled "Mooney" in the tables.
[0141] (b) The Shore A hardness: measurements carried out according
to Standard DIN 53505.
[0142] (c) The tensile tests make it possible to determine the
elasticity stresses and the properties at break.
[0143] Unless otherwise indicated, they are carried out in
accordance with French Standard NF T 46-002 of September 1988.
Processing the tensile recordings also makes it possible to plot
the curve of modulus as a function of the elongation, the modulus
used here being the nominal (or apparent) secant modulus measured
in first elongation, calculated by reducing to the initial
cross-section of the test specimen. The nominal secant moduli (or
apparent stresses, in MPa) are measured in first elongation, at
60.degree. C..+-.2.degree. C., at 10%, 100% and 300% elongation,
respectively denoted MSA10, MSA100 and MSA300. The breaking
stresses (BS) in MPa and the elongations at break (EB) in % are
measured at 60.degree. C..+-.2.degree. C. according to Standard NF
T 46-002.
[0144] (d) The dynamic properties .DELTA.G* and tan(.delta.)max are
measured on a viscosity analyser (Metravib VA4000) according to
Standard ASTM D 5992-96. The response of a sample of vulcanized
composition (cylindrical test specimen with a thickness of 2 mm and
a cross-section of 79 mm.sup.2), subjected to a simple alternating
sinusoidal shear stress, at a frequency of 10 Hz, under standard
temperature conditions (23.degree. C.) according to Standard ASTM D
1349-99 or, as the case may be, at a different temperature
(60.degree. C.), is recorded. A peak-to-peak strain amplitude sweep
is carried out from 0.1% to 50% (outward cycle) and then from 50%
to 0.1% (return cycle). The results made use of are the complex
dynamic shear modulus (G*) and the loss factor tan .delta.. The
maximum value of tan .delta. observed (tan(.delta.)max) and the
difference in complex modulus (.DELTA.G*) between the values at
0.1% and 50% strain (Payne effect) are shown for the return
cycle.
2.2--Example
[0145] In this example, the two elastomers SBR A and SBR B were
used for the preparation of rubber compositions A and B, each
comprising carbon black as reinforcing filler.
[0146] Each of these compositions A and B exhibits the following
formulation (expressed in phr: parts per hundred parts of
elastomer):
TABLE-US-00001 Elastomer 100 N234 54 Paraffin 1 Antioxidant (1) 4
Stearic acid 1.5 ZnO 3 Sulphur 1.3 Accelerator (2) 1.3 (1)
N-(1,3-dimethylbutyl)-N-phenyl-para-phenylenediamine (6-PPD) (2)
N-cyclohexyl-2-benzothiazolesulphenamide (CBS)
[0147] Each of the following compositions is produced, in a first
step, by thermomechanical working and then, in a second finishing
step, by mechanical working.
[0148] The elastomer, the black, the paraffin, the antioxidant, the
stearic acid and the zinc monoxide are successively introduced into
a laboratory internal mixer of "Banbury" type which has a capacity
of 400 cm.sup.3, which is 75% filled and which has an initial
temperature of approximately 70.degree. C. The stage of
thermomechanical working is carried out for from 5 to 6 minutes, up
to a maximum dropping temperature of approximately 160.degree. C.
The abovementioned first step of thermomechanical working is thus
carried out, it being specified that the mean speed of the blades
during this first step is 70 revolutions/min.
[0149] The mixture thus obtained is recovered and cooled and then,
in an external mixer (homofinisher), the sulphur and the
accelerator are added at 30.degree. C., the combined mixture being
further mixed for a time of 3 to 4 minutes (abovementioned second
step of mechanical working).
[0150] The compositions thus obtained are subsequently calendered,
either in the form of plaques (with a thickness ranging from 2 to 3
mm) or of thin sheets of rubber, for the measurement of their
physical or mechanical properties. The vulcanization is carried out
at 150.degree. C. for 15 minutes.
[0151] The properties of these two compositions are compared with
one another, both in the non-vulcanized state and in the vulcanized
state. The results are given in the following table:
TABLE-US-00002 Composition A B Elastomer SBR A SBR B ML (1 + 4) 83
87 100.degree. C. (elastomer) Properties in the non-vulcanized
state: MS(1 + 4) 55 58 100.degree. C. (mixture) Properties in the
vulcanized state: Shore A 66 66 MSA10 6.73 6.47 MSA100 2.75 2.70
MSA300 5.32 5.41 MSA300/MSA100 1.93 2.00 Losses 60.degree. C. (%)
26 23 Tension: BS (MPa) 20 19 EB (%) 386 362 Dynamic properties as
a function of the strain: .DELTA.G* (MPa) at 1.45 1.27 60.degree.
C. Tan.delta..sub.max at 0.170 0.155 60.degree. C.
[0152] It should be noted that the composition B according to the
invention, based on the said functionalized block copolymer,
exhibits a "mixture" Mooney value similar to that of the control
composition A based on the functionalized SBR A. The composition B
according to the invention and the control composition A thus
exhibit an equivalent processability in the non-vulcanized
state.
[0153] As regards the properties in the vulcanized state, the
composition B according to the invention and the control
composition A exhibit equivalent properties, except for the losses
at 60.degree. C. and the dynamic properties. This is because the
composition B according to the invention exhibits values of losses
at 60.degree. C., of .DELTA.G* and of Tan.delta..sub.max. at
60.degree. C. which are lower than those of the control composition
A. The hysteresis properties of the composition B according to the
invention are thus improved, with respect to those of the control
composition A.
[0154] In other words, the composition B according to the
invention, based on the said functionalized block copolymer B,
exhibits improved rubber properties in the non-crosslinked state
and in the crosslinked state, with respect to those of the
composition A based on the functionalized SBR A, as a result of a
markedly reduced hysteresis at equivalent processing.
* * * * *